title: Visualizing virus assembly intermediates inside marine cyanobacteria.
abstract: Cyanobacteria are photosynthetic organisms responsible for ∼25% of organic carbon fixation on the Earth. These bacteria began to convert solar energy and carbon dioxide into bioenergy and oxygen more than two billion years ago. Cyanophages, which infect these bacteria, have an important role in regulating the marine ecosystem by controlling cyanobacteria community organization and mediating lateral gene transfer. Here we visualize the maturation process of cyanophage Syn5 inside its host cell, Synechococcus, using Zernike phase contrast electron cryo-tomography (cryoET). This imaging modality yields dramatic enhancement of image contrast over conventional cryoET and thus facilitates the direct identification of subcellular components, including thylakoid membranes, carboxysomes and polyribosomes, as well as phages, inside the congested cytosol of the infected cell. By correlating the structural features and relative abundance of viral progeny within cells at different stages of infection, we identify distinct Syn5 assembly intermediates. Our results indicate that the procapsid releases scaffolding proteins and expands its volume at an early stage of genome packaging. Later in the assembly process, we detected full particles with a tail either with or without an additional horn. The morphogenetic pathway we describe here is highly conserved and was probably established long before that of double-stranded DNA viruses infecting more complex organisms.
authors.affiliation: National Center for Macromolecular Imaging, Verna and Marrs Mclean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Dai
authors.forename: Caroline
authors.initials: C
authors.lastname: Fu
authors.forename: Desislava
authors.initials: D
authors.lastname: Raytcheva
authors.forename: John
authors.initials: J
authors.lastname: Flanagan
authors.forename: Htet A
authors.initials: HA
authors.lastname: Khant
authors.forename: Xiangan
authors.initials: X
authors.lastname: Liu
authors.forename: Ryan H
authors.initials: RH
authors.lastname: Rochat
authors.forename: Cameron
authors.initials: C
authors.lastname: Haase-Pettingell
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Piret
authors.forename: Steve J
authors.initials: SJ
authors.lastname: Ludtke
authors.forename: Kuniaki
authors.initials: K
authors.lastname: Nagayama
authors.forename: Michael F
authors.initials: MF
authors.lastname: Schmid
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: King
authors.forename: Wah
authors.initials: W
authors.lastname: Chiu
mesh_terms: D059001:Aquatic Organisms / Q000166:cytology / Q000648:ultrastructure / Q000821:virology; D001435:Bacteriophages / Q000254:growth & development* / Q000648:ultrastructure*; D020285:Cryoelectron Microscopy / Q000379:methods*; D055032:Electron Microscope Tomography / Q000379:methods*; D008954:Models, Biological; D046940:Synechococcus / Q000166:cytology / Q000648:ultrastructure* / Q000821:virology*; D019065:Virus Assembly